rx8wannahave

First, relax...I don't have the know how nor the metal working skills to build such a thing. That's not what I'm really talking about...

I'd rather have a NA engine than a Turbo or SC since it seems a NA rotary would last longer.

I know there is a company out there, I think in NJ, that builds 3-rotor engines. BUT, if you wanted to save money and build yourself a 3-rotor Renesis based engine what would you need to do?

I know the E-shaft (if I remember the right name) would have to be changed and suspect:

*some type of custom bracket/block to connect the new rotor
* a new header, intake manifold
*new ECU?
*motor mount?
*move some things around for space (maybe)?
*new tranny?
*new rear end?

As a newbie regarding the rotary and the details of engines overall, what would you have to do to build such a engine? I'm guessing this is not an easy task or else more people would be talking about it but to keep up with the Turbo & SC people another rotor would probably be the only real NA way.

I wish it was a matter of a new e-shaft and rotor housing but that's my wishful thinking.

Please be as detailed and technical as you want, I'm trying to learn here. Is my dream super far fetched or do you all think in time there will be an "easy build kit" for making our Renesis a 3-rotor?

Thanks in advance for the rotary wisdom!

vectorwolf

I think this engine would actually be considered a "20b" (which basially means it's a 2.0 litre engine, just as our 13b is a 1.3 litre engine!). But... I think the fact that our ports are built into the sides of the chambers rather than the periphery (or the "outer wall"), you'd have to use a middle rotor from an older engine? The eccentric shaft would need to be longer to fit through all three... and that's about all I could say. lol

This is something I'd seriously like to know as well. NA all the way.

ZoomZoomH

iTrader: (1)

btw once it's 3 rotor it is called 20B in Mazdaspeak....

edit: pwned by slowness

vectorwolf

^ I win!

tuj

If you were to try to do this with Renesis parts, you would still need to machine a new intermediate housing. The ports in the end-housings are bigger and different than the ports in the intermediate housing, so two intermediate housings would result in the middle rotor not getting enough air.

Of course, custom e-shaft, manifolds, etc. More cost effective to source a 20b. If you were to peripheral port it (both intake and exhaust), it would be easier as you wouldn't need two different intermediate housings.

rx8wannahave

Ohhhhhhhhh, thanks VectorWolf...you too ZoomZoomH, no "pwned" intended...lol

Thanks, I think I understand what you all are saying. But...I thought that the "side port" made the Renesis more efficient. Is that true? Since the Renesis is the most modern rotary engine we have I thought it would be better to start there.

What I would worry about with the 20B is that I would have to then change a whole lot of other things to make it work. Where do you get a tranny from, ECU, etc?

Teach me more...

ZoomZoomH

iTrader: (1)

the side intake/exhaust port is mainly designed to improve exhaust emissions of the rotary engine

to make *real* power, peripheral ports (both intake AND exhaust) are still the preferred design (see Sportbook ALMS prototype 20B race motor )

rx8wannahave

By the way, can I go some place and buy a rotary engine (Renesis hopefully) model that I could take apart to see the guts of the engine. There is no better way to understand all of this than to see what I'm working with.

Is there a place online or a plastic Renesis engine you can build/take apart/etc so you can learn the details of it. Maybe Mazda would not allow such a thing...but it sure would help me learn more about the rotary engine.

Hmmmm....I wonder how much a Renesis engine taken out of a poor busted up RX8 from a junkyard cost. Hmmmm....

ZoomZoomH

iTrader: (1)

http://www.rotaryengineillustrated.com/

KYLiquid

you can get a renesis motor from a couple places for around 2500 for a rebuilt one (3500 with out a core return) so I would thing you could get a damaged one for half that.

rx8wannahave

Thanks for the link, I just learned a bunch and I think I can see what you mean regarding adding another rotor. While...I still think it's possible and "MIGHT" be cheaper than a Turbo or SC...but what do I know.

I saw that I would need a new oil pan also if you added a rotor. I would love to learn how to work with metal.

By the way, the Renesis is built out of Iron right??? Why not a lighter metal? Too hot I guess?

tuj

The real 20b engine from the Cosmo saloon is a side-intake, perhipheral exhaust engine with 2 turbos. The Cosmo only came with an AT transmission, although the TII and FD transmissions can be adapted from what I understand.

The 20b will fit in the RX-8 and a couple people have done it, but say goodbye to your ABS/TSC/DCS. There are several aftermarket ECU's that can run a 3 rotor, and that's probably a better option than retaining the Cosmo ECU. Be warned; 20b engines are getting more rare and more expensive.

You can get a full peripheral port 20b from Mazdaspeed for $$$ or I bet Downing would sell you one for like 20 grand. The other option is to piece together a 3-rotor using 13b housings and one of the wider 20b intermediate housings. You'd still need intake, exhaust, and e-shaft, but its probably cheaper than a 20b if you know what you're doing.

As far as the side ports go, Mazda has used side intake and perhipheral exhaust on most of their motors before the Renesis. The true power applications use peripheral intake ports which make more high-end power, at the expense of idle and low end quality. And by high-end, I mean over 5k! Great for race motors, not for the street.

The new side exhaust ports on the Renesis result in the engine having zero overlap, which is actually quite beneficial for forced induction. The Renesis has basically increased 100 hp over the last 13b in NA form without any more displacement and a ten-fold decrease in emissions.

carbonRX8

iTrader: (1)

Acording to a post on here some where by Boostd7 (site owner) the next issue of Rxtuner will have an article on this very topic. Get the mag.

Acostia is the place you were talking about in NJ

therm8

A 3 rotor 13B is not really a 20B. It's a custom built engine, that happens to be approximately 2.0L. A 3 rotor MSP 13B is definately not a 20B.

Here's a custom 13B 3 rotor: http://www.hitman.hm/rx7.htm

vectorwolf

Why do you lose all of the electrical stuff when switching engines?

tuj

The TCS/DSC are controlled by the ECU. I suppose you could leave the stock ECU hooked up and use something like an interceptor to fool it into thinking the stock engine is still hooked up, but I really doubt that would work. AFAIK, the ABS controller is integrated in the ECU also. The tach and speedo signals are from the ECU also I believe.

brillo

I had kicked around with RG what it would take to build a 3rotor Renesis engine from existing parts in the “cheapest” way possible. Bear in mind, the following is cheap only in the sense that I tried to use as few custom parts as possible. This is theoretically possible but not proven to work. Its also not the optimum design, but again, I was going for off the shelf parts.

First I would start with a 4port Renesis engine. I would then add another Renesis rotor and rotor housing. The tricky part is the second intermediate housing. I would get a 20B large intermediate housing and after filling in the extra seal grove area (and lapping it smooth) so it will mate up with the Renesis housings, I would make 2 custom side exhaust ports, one large and one small. This way the center rotor will breath and exhale the same as the out rotors. So your side exhaust ports would look like this.

“L” Rotor Housing “S” “S” Rotor Housing “L” “S” Rotor Housing “L”

Obviously, the most time, money an expense would have to go into this 20B intermediate housing. I think the side exhaust ports could be drilled out and made to work.

You could use a off the shelf 3 rotor eccentric shaft, but it would have to be rebalanced as the Renesis rotors weigh less. I would fab a simple box collector header (like the stock manifold) for the exhaust first, I know its not the best for flow, but the idea is cheap and getting the car to run. I would try to use the stock 20B intake manifold with some changes, if that doesn’t work, I’d create a simple manifold with 3 TB (one for each rotor). I would lose the stock oiling system and go pre-mix for simplicity. I would source a motec or a microtech for management duty.

All of this uses modified off the shelf parts. The real cost would be the work to the intermediate housing, balancing the eshaft and the manifold creation. This is not the optimum solution, the manifold design would not be optimal and you could argue that those smaller side exhaust ports are still hurting power.

This is a gross simplification, but I think in theory all this should work together.

tuj

The real cheapest way to get a 3-rotor Renesis is to wait until Mazda makes it.

beachdog

Skip the three rotor and go for four. "Just" siamese two Renesis together front to back.

BTW, there is an old model kit in the "Visible" series of the rotary engine. Just google visible rotary.

tuj

Yeah that doesn't work too well. Check out granny's speed shop and their home-made 4-rotor from two 13b's that used a keyway and a tapered coupling to join the two e-shafts. It works, but it doesn't have the real smoothness since the rotors are spaced 180 degrees, unless you cant one of the engines 90 degrees. You'd also HAVE to go peripheral port for that to work. They eventually determined it was too much trouble and went with a big Chevy motor.

rx8wannahave

Yeah, but all the talk regarding the Mazdaspeed 8 (if it EVER comes out) talks about Turbo or SC...or, the latest...wider rotors?

:0(

Thanks everyone for your comments, I learn a bunch here.

If I had the know how to work with metal (add rotary engines, engine management, etc lol), I would invest into figuring this out because 3-rotors just sound right to me.

Come on Mazda...heck, if you make it a 1L 3-rotor I think we all would be happy. 1L 325HP 3-rotor Renesis engine. Ohhh mama...

Philip_SA

Where will rotary development go. If looking at formula 1 technology, I will think they must go with more rotors and maybe smaller or same as 13B size but not wider.
think of a peripheral port, what more can be done, I dont thing too much, just lighten everything, you cant get more mixture in (excluding turbos)
so why not go more rotors
wider maybe makes more torque, but ..... revs...power

beachdog

If you look at the Mazda showcars, the rotary is going to be the powerplant for pure hybrids ie the internal combustion engine only runs the generator.

Think about it, they tune the rotary for maximum power to weight to efficiency. The only power that goes to the wheels comes from an electric motor. The cure for the rotary torque issue. Infinite torque at 0 RPMs.

tuj

This is completely wrong. Passenger cars are quite a world away from Formula 1. Obviously having more combustion chambers per a set amount of displacement yields better efficiency, but at the expense of added complexity and cost. Look at the F22C versus the LS7 engines. The F22 is getting near 120 hp / L, while the LS7 is more like 70 hp / L, but the LS7 is not all that much bigger or heavier while making twice the hp.

If what you were saying was true, we should all be riding around in 14 cylinder 2L engines. They probably would sound wicked, but it would be hard to justify the complexity and cost. The wider rotor width IS a good idea; the resulting engine will make at least as much torque and hp, all at a lower RPM. And we all know that even if torque drops off, hp is still increasing.

Don't get me wrong; I would love a 3 rotor as much as anyone else, but it introduces several complexities (multi-piece e-shaft) that increase cost significantly.

rx8wannahave

I was dreaming about this again...and I needed this thread to bring back to reality...



I hope a wider 13B (15B I guess) and direct fuel injection can cure my ills....lol. Trying my best to avoid a future Turbo upgrade...but it seems the chips are stacked against me.

I love NA power, but it seems I will have to give in...in the future.